Over a few exceptionally warm days last July, Greenland’s frozen surface turned into a colossal puddle. Even the coldest parts of the world’s largest island saw ice thaw and rain fall, fuelling concerns over the future of glaciers that hold enough water to raise global sea levels by around 7 metres.

A record of the past written in an ancient ice core now reveals that Greenland’s ice sheet is not melted as easily as some fear. But the message is not entirely reassuring: it also implies that Antarctica has much greater potential to raise sea levels than previously thought.